This invention relates to an improved hydrophilic coating for insertable or implantable medical devices comprising an antiblock agent.
Water soluble, biocompatible compounds that impart lubricity to the surface of otherwise non-lubricious materials are desirable for use on medical devices which are inserted or implanted into the body. Such medical devices may include catheters that are utilized to deliver a stent, stent-graft, graft or vena cava filter, balloon catheters, other expandable medical devices and so forth. The industry has turned to hydrophilic lubricious coatings in order to overcome problems with commonly used hydrophobic coatings such as silicone, glycerine or olive oil.
Hydrophobic coatings, like silicone, have been known to wash off when exposed to an aqueous environment, lose initial lubricity rapidly, and lack abrasion resistance. Residual amounts of silicone have also been known to cause tissue reaction and irritation in patients. The loss of lubricity can lead to discomfort during insertion into a patient, and damage to blood vessels and tissues due to frictional forces during insertion or removal of the device.
Hydrophilic compounds that are biocompatible or blood compatible are more readily discharged from the body and have less of a tendency to cause tissue irritation.
One class of polymeric substances that dissolve or swell in an aqueous environment, often referred to as xe2x80x9chydrogels,xe2x80x9d are capable of manifesting lubricity while in a wet state, and are popularly utilized as lubricious coatings for medical devices. When hydrated, these substances have low frictional forces in humoral fluids including saliva, digestive fluids and blood, as well as in saline solution and water. Such substances include polyethylene oxides (optionally linked to the substrate surface by interpenetrating network, IPN, with poly(meth)acrylate polymers or copolymers; copolymers of maleic anhydride; (meth)acrylamide polymers and copolymers; (meth)acrylic acid copolymers; poly(vinyl pyrrolidone) and blends or interpolymers with polyurethanes; and polysaccharides.
These water soluble coating materials, while popular because they provide excellent lubricity and biocompatibility, may be sensitive to moisture.
A problem associated with the moisture sensitivity of such hydrogels is that they may prematurely uptake ambient moisture and become sticky or tacky. This results in what is referred to in the industry as a xe2x80x9cself adhesionxe2x80x9d effect. This can result in undesirable adhesion of the medical device to itself via the coating, to other devices, or to any other surface to which it comes in contact during sterilization or storage. In the case of dilatation balloons, after sterilization or storage hydrogel coatings on the folded section of the balloon can stick to themselves. This will lead to pinhole failure upon expansion of the balloon.
Metal wires, such as guide wires, may be coiled. The xe2x80x9cself adhesionxe2x80x9d effect can lead to removal of some of the coating or to failure of the coating from the surface of the wire as it is uncoiled.
These problems are discussed in U.S. Pat. No. 5,509,899 issued Apr. 23, 1996 to Fan et al. Fan et al. teaches a medical balloon and catheter which is wrapped and folded upon itself and in which the balloon is free of bridging and adhesion between abutting surfaces. The balloon has a base of a continuous polymeric surface which is expandable. On the polymeric surface is disposed a lubricious, biocompatible hydrogel coating and a thin, lubricious, blood-compatible coating is disposed on the hydrogel coating and adheres to it to prevent abutting surfaces of the folded polymeric surfaces from adhering to each other during inflation and to prevent delamination of the hydrogel coating and/or rupture of the balloon. Preferably, the blood-compatible coating is polyethylene glycol, methoxy polyethylene glycol or mixtures thereof having a molecular weight of between about 100 and 20,000. The blood-compatible coating is applied as an anti-blocking agent. See column 2 lines 18 to 37. However, application of a second coating can be costly.
The present inventors have found a hydrophilic, biocompatible coating for medical devices which avoids the aforementioned problems. The hydrophilic lubricious coating of the present invention comprises an antiblock additive which migrates to the surface of the coating, thereby impeding blocking or sticking of two surfaces and improving the performance of the medical device.
The present invent relates to medical devices which are designed for insertion or implantation into the body, and which device has at least one surface which periodically comes into contact with a second surface. The first surface is coated with a lubricious hydrophilic polymeric coating, and the coating also comprises at least one antiblock agent.
The antiblock agent blooms to the surface of the hydrophilic coating forming a protective layer on the surface to prevent self adhesion of the hydrophilic coating.